1. Field of the Invention
The present invention relates to liquid ejecting apparatuses. More specifically, the present invention relates to a liquid ejecting apparatus including an ink jet recording apparatus for forming dots on a recording medium by discharging ink droplets from nozzles in an manner correspondingly to print data.
2. The Relevant Technology
Ink jet recording apparatuses perform printing operations by ejecting inks onto recording paper and are known as liquid ejecting apparatuses. Currently, the ink jet recording apparatuses are used in many types of printing, including color printing since the ink jet recording apparatuses produce relatively small noise during operation and can form small dots at high density.
An ink jet recording apparatus of the above type typically includes an ink jet printing head that is supplied with inks from ink cartridges, and a paper feeding mechanism for moving a recording medium in the scanning direction of the printing head as well as in a vertical direction. The ink jet recording apparatus performs recording by discharging ink droplets onto the recording medium. The ink droplets are discharged by generating a mechanical pressure or thermal energy to the printing head, while moving the printing head on a carriage in a width direction (main scanning direction) of the recording medium. The printing head on the carriage can discharge color inks such as black ink, yellow, cyan, and magenta. The ink jet recording apparatus can perform not only text printing with black ink, but also full color printing by changing a discharge ratio of the inks.
Additionally, in order to increase print quality in color printing, current ink jet recording apparatuses may use a total of six inks including black, yellow, cyan, and magenta, as well as light cyan and light magenta. Furthermore, ink jet recording apparatuses have been developed which are capable of large volume printing using large sized paper. In order to supply the increased amount of ink required for the increased volumes, the capacities of ink cartridges for supplying inks to portions of a printing head have been enlarged. For example, an ink jet recording apparatus has been developed in which removable ink cartridges are located in cartridge holders disposed in fixed locations at both ends of the apparatus instead of being located on the carriage. The ink is supplied from the cartridge holders to the printing head through ink flow paths comprised of flexible tubes or the like.
Such ink jet recording apparatuses print by pressing inks in pressure generating chambers which are located in each printing head. The pressurized ink is discharged as ink droplets to a recording medium such as recording paper. Unfortunately, however, misprinting may occur due to an increase in ink viscosity and ink fixation, caused by evaporation of solvent from nozzle openings together with dust adhesion and the mixing of air bubbles. Accordingly, the ink jet recording apparatuses generally include a capping unit in order to prevent ink from drying by sealing the nozzle openings of the printing head when no printing is being performed.
The capping unit functions as an air sealing cover for preventing ink in the nozzle openings from drying when no printing is being performed, that is, when printing is stopped. The capping unit also functions by sealing nozzle plates when the nozzle openings clog, and by using negative pressure from a suction pump connected to the capping unit to suction ink from all the nozzle openings. Thus the capping unit is able to eliminate clogging caused by ink fixation in the nozzle openings as well as ink discharge defects caused by the mixing of ink in an ink flow path.
A “cleaning operation” is another function commonly used in ink jet apparatuses and is accomplished by applying suction force in order to exhaust excess or residual ink in order to eliminate clogging in the printing head and the mixing of air bubbles into the ink flow path. Typically, the cleaning operation is automatically executed when printing is restarted after the apparatus is stopped for a long time, and when a user manually operates a cleaning switch in order to eliminate quality deterioration.
The ink jet recording apparatus also has a “flashing operation” function comprised of discharging air droplets from all the nozzles while applying a driving signal that is unrelated to the printing head. This flashing operation is automatically executed according to a predetermined period. The flashing operation aligns irregular meniscuses in the vicinity of the nozzle openings of the printing head which may be caused by wiping or other portion of the cleaning operation. The flashing operation prevents clogging issues caused by increased ink viscosity in the nozzle openings from which less amount of ink is discharged during printing.
With in the ink jet recording apparatus, cartridges can be replaced depending on the printing purpose since the ink jet recording apparatus can perform various types of printing. More specifically, when printing needs to be performed using different inks than the colors presently loaded in the ink cartridges, the loaded cartridges may be temporarily removed, and replaced with ink cartridges containing inks of desired types. Thus, printing may easily and frequently be performed with different types of print qualities using the same printer and different types of inks.
Typically, when a type of ink is switched to a different type of ink, a washing liquid used for temporarily washing the remaining ink in a flow path is introduced into a recording head before the different type of ink is used. Additionally, in order to prevent the formation of dried ink in the nozzle opening when the apparatus is stopped, a moisturizing liquid for preventing drying is discharged into the capping unit before the capping function is performed.
Accordingly, the ability to switch between inks and functional liquids such as washing liquid or moisturizing liquid has been proposed. Unfortunately, however, immediately after a liquid cartridge is switched, a liquid of the previously loaded cartridge still remains in the ink flow path and the printing head. Thus, print quality is deteriorated after replacement. Additionally, the mixing of liquids of different types may cause problems such as an undesired chemical reaction, increased ink viscosity, and clogging. Presently, the flashing and cleaning operations currently used cannot cope with these problems.
Several technologies have been developed to solve these problems, including the apparatuses described in Japanese Patent Applications JP-A-2001-219574 and JP-A-2003-220798 which each describe an ink jet recording apparatus with a plurality of fluid supply units and a switching unit for selecting an arbitrary number of fluid supply units from among the plurality of fluid supply units, in order to prevent different types of inks from being mixed.
Although each of the described apparatuses efficiently uses a liquid switching unit, the complete switching of a liquid in a flow path still requires a certain period of time. Additionally, neither system includes a unit for confirming that the liquid in the flow path has completely been switched or a unit for confirming defective ejection immediately after liquid switching. Accordingly, there remains the possibility that a problem may occur in reliability of initial print quality immediately after liquid switching.